1. Field of the Invention
This invention relates to plural component coating application systems and more particularly to compressed gas flushing systems used to clean the component delivery portions of plural component coating application systems.
2. Background
U.S. Pat. No. 5,458,683 to Taylor, et al. discloses a pipeline treating apparatus having a pair of pivotally mounted housing sections and a pair of separately pivotal nozzle frames. A drive mechanism on the nozzle frames oscillates the nozzle plate a predetermined arcuate distance around the circumference of the pipeline so that the nozzles treat the entire outer surface of the pipeline. A travel unit drives a cleaning unit along the pipeline, while a motor oscillates the nozzles. Taylor does not disclose variation of the oscillation frequency or the rate of travel based on flow rate.
U.S. Pat. No. 6,881,266 to Daykin et al. discloses an apparatus for spraying a coating onto the outside of a pipe includes a body for mounting on a pipe to be coated. A spray gun is mounted on the body such that it can move relative to the body to spray coating completely around the periphery of the pipe. The spray gun includes a nozzle with a rotating tip and an actuator for rotating the tip, the tip being rotatable between a first position producing a fan-shaped spray, and a second position producing a jet spray. Preferably there is only one spray gun, the coating applied completely around the periphery of a pipe using only one spray gun, the body of the apparatus remaining rotationally fixed relative to the axis of the pipe. The spray gun may be movably, especially pivotally, mounted on the ring so that it may be moved, especially turned, to spray away from the surface of a pipe, for example through 90° to spray tangentially to the pipe. Daykin does not disclose a method or apparatus for spraying away from the surface of a pipe for reversing and feathering and does not disclose a method or apparatus for use of more than one spray guns capable of coordinated flipping in both clockwise and counterclockwise directions.
U.S. Pat. No. 7,066,186 to Barr discloses a method and apparatus mounted on a painting system to clean a paint feed line by forcing a solvent and an inert gas, nitrogen, through the feed line at the end of a cleaning stage, the gas remaining in the feed line until the next operational stage begins. Bahr discloses a system for single component coating materials or coating materials that have been pre-mixed and have a long pot life. It is not clear whether the system works with plural component coatings with a rapid cure time and a pot life that is measured in seconds. A solvent is used prior to injection, at relatively low pressure, of an inert gas. Since there is no mixing manifold, cleaning of a mixing manifold or static mixing tubes is not disclosed.
U.S. Pat. No. 6,227,228 to Fullenbach discloses a purge process for sequential plural component mixing system, alternately injecting water and air at intervals into the mix chamber through purge valves to purge the mixed material. Fullenbach's disclosure appears to be limited to hydro-softfeel lacquers and not with epoxy and urethane coatings. Further, a combination of air and water is used to flush one side of a mixing manifold, use of inert gas only is not disclosed.
German Pat. DE 4134598 to Blochmann, et al. discloses a method of cleaning a viscous material mixer by directing a blast of compressed air through a mixer and then a blast of a mixture of air and solvent. Blochman discloses blasting at high pressure, a single pressure purge. Blochman does not disclose performing a high pressure followed by a low pressure purge.
Plural component coating systems such as Polyurethane and Epoxy coatings consist of two components that are mixed together at a specific ratio and applied using airless hot-spray equipment. Often these coatings are solvent free, consisting of 100 percent solids.
The two-components, referred to as component A and component B are stored in separate containers and have an extended shelf life.
Once component A and component B are mixed together in the prescribed ratio, a chemical reaction begins to occur that will ultimately cause the material to adhere to the substrate, harden and become the desired corrosion barrier. This is a “curing” process as opposed to a “drying” process brought about by the evaporation of solvents or water contained in the coating. This curing is not instantaneous but occurs over time and passes through several stages.
A first identifiable point is referred to as “pot life”, or the amount of time after mixing before the material begins to cure. This is often only a matter of seconds in the case of polyurethane and epoxy coatings. The second point is “touch dry” where the coating appears dry to the touch but can still be easily damaged by handling or placing objects on the coated surface. The third point is “stackable”. When the coating reaches this condition it can be handled easily and is not subject to damage when other similar items are stacked on top of it. The final point is “fully cured” and is the point where no further chemical reaction will occur.
The rate the coating passes through the various points depends on many variables, some of which are: a) the type of coating, polyurethane coatings cure more rapidly than epoxy coatings; b) the chemical composition of component A and B, coatings can be chemically designed to cure more rapidly or slowly; and c) the ambient temperature, the higher the temperature the faster the curing reaction occurs. The curing of the coating material creates problems for airless hot-spray application.
In one example, a drum of Component A, which is typically pasty at ambient temperature, is heated by an electric heater (bottom plate or drum belt) to about 50° C. At this temperature the viscosity of component A significantly decreases and becomes similar to that of component B. Component B, typically liquid at ambient temperature, usually requires no extra heating prior to pumping into the device. Both components are transported from the drums to the high pressure dosing or proportioning pumps by individual material feed pumps and material hoses. In general, the feed pumps are pneumatically operated piston pumps.
The high pressure dosing pumps are an important element of the spraying device. There are different systems which are mainly based on combinations of pumps with different volumes or pumps with different stroke length and/or stroke speed. In some examples, the dosing pumps pressurize the material to an operational spraying pressure of at least 3000 psi. In separate lines and in exact proportions of mixing ratio, the two components are pushed through the high pressure fluid heaters and gauge to a mixing block.
Depending on the kind of employment of the device, on the required length of the hose package (separate hoses for component A and B) and on the pot life of the material to be sprayed, the mixing block is mounted on the frame of the proportioning unit or is located separately. The mixing block can include manually or pneumatically controlled valves to open and close or to bypass the fluid lines. In case the mixing block is placed beyond a certain distance from the machine, the hose package is heated (electrically, by hot water, etc.). In the mixing block, the two components are mixed by a static mixer. The chemically reacting two component blend then passes through a high pressure hose. Various types of manually or mechanically controlled spray guns can be connected to the dispensing hose.
The rapid curing of the coating material requires that the mixed material be purged out of the system each time the equipment stops. Otherwise, the coating material will set up in the lines and spray tips. If the coating material sets up in the system then extensive and time consuming repairs have to be made before work can restart.
Continuing with the example, the mixing block also has a flushing system to pump out the mixed material when spraying has to be temporarily interrupted or stopped. A powerful solvent flushing or purging pump is activated when the system is set to ‘flushing mode’ and the spray gun trigger is pressed. The mixed material is forced out by the solvent, which also flushes and rinses all system components, which were in contact with the processed material, such as the static mixer, the high-pressure hose and the spray gun. This flushing process is intended to prevent blocking of the device by cured material.